So final semantics provides concrete natural and uniform ways of structuring by-simulation. And the functors suggests themselves the shape that by-simulations should have. What do we gain? Well we gain general theorem in this perspective a uniform proofs for one by-simulation is a congruence. So, here we see how this general concept in this metamodel which focuses, brings to the foreground the concept of a transition system that is underlying the dynamic behaviour of many computational objects can allow to factor out a given class of proofs, namely those which show that by-simulation is a congruence.

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